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Contract No. DE-AC36-08GO28308

An Analysis of Plug Load 

Capacities and 

Power Requirements in 

Commercial Buildings

Preprint

Michael Sheppy, Paul Torcellini, 

and Luigi Gentile-Polese

National Renewable Energy Laboratory

To be presented at the 2014 ACEEE Summer Study on Energy 

Efficiency in Buildings

Pacific Grove, California

August 17–22, 2014

Conference Paper

NREL/CP-5500-61528

August 2014
NOTICE

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An Analysis of Plug Load Capacities and 

Power Requirements in Commercial Buildings

Michael Sheppy, Paul Torcellini, Luigi Gentile-Polese 

National Renewable Energy Laboratory

ABSTRACT

Plug and process loads (PPLs) are a critical part of any building, because they enable 

much of its functionality. PPLs are defined as loads that are not heating, ventilation, air 

conditioning or lighting. Examples include desktop computers, telephones, desktop accessories, 

and kitchen appliances. Many PPLs, such as workstation equipment, are controlled or specified 

by the tenants of commercial office buildings. Tenants require that sufficient electrical power is 

available for PPLs to meet the maximum anticipated load. Lease language thus often dictates a 

value of 5 to 10 W/ft2 for PPLs. However, measured data show that actual loads are much lower 

than this, but prospective tenants and real estate brokers lack adequate references to encourage a 

change in the power capacity that is typically requested. 

Overestimating PPL capacity leads designers to oversize electrical infrastructure and 

cooling systems. Better guidance would enable improved sizing and design of these systems 

resulting in more energy-efficient electrical and HVAC systems while saving upfront capital 

costs. Ultimately, this saves the occupant money in reduced rents because the owner does not 

need to recover the additional infrastructure costs. This paper shows measured evidence that 

actual peak PPL densities are significantly lower (by a factor of 5 to 10) than what is typically 

requested, negotiated, or required in leases. 

Introduction

Plug and process loads (PPLs) provide much of the functionality of a building. They 

represent the computers and their related networks, telecommunications, security, personal 

amenities, and kitchen equipment. Any load that is not heating, ventilation and air conditioning 

(HVAC) or lighting is categorized as a PPL. Designing for PPLs can be difficult due to their: 

huge variety, sheer number, and small individual magnitudes. PPL power requirements are 

frequently overestimated because designers often use estimates based on “nameplate” data. To 

be conservative, design teams overestimate PPLs for equipment sizing to avoid undercooling or 

underpowering a space. The oversizing has been a long-standing issue and peak PPL estimates of 

5 to 10 W/ft2 are commonplace in the industry (see Table 1 below). 

One important result of oversizing electrical distribution is that cooling, fan, and 

ductwork systems are also oversized thus increasing initial construction costs. From an energy 

perspective, the oversizing causes equipment to operate at part load, which is often less efficient 

and can cause zone temperature fluctuations that create discomfort. Transformers also become 

less efficient at part-load performance (see Figure 1). Thomas and Moller (2007) found that 

rightsizing chillers in two buildings reduced whole-building energy use by 3% to 4%. If an 

integrated design approach could enable 3% whole-building energy savings in all U.S. office 

buildings stock, it could save 34 TBtu of site energy per year—an energy savings that could be 

achieved without additional capital investment.
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Figure 1. Systems that are affected by plug and process load densities specified in lease agreements. 

(Figure credit: Alfred Hicks/NREL)

Plug and Process Load Densities Reported in the Literature

Brokers suggest PPL density needs as high as 16 W/ft2 as part of the lease structure 

(CBEA 2012). The available literature suggests that companies and institutions are specifying 

lower PPL capacities in their leases. For instance, in 2012, the U.S. General Services 

Administration (GSA) changed its standard lease requirements from a 7 W/ft2 minimum to a 

4 W/ft2 minimum for PPLs (Pentland 2011; GSA Public Buildings Service 2011; GSA 2013) as 

part of its government-wide efforts to create green, sustainable buildings. Table 1 summarizes 

the PPL densities reported in the literature. The reported PPL densities show significant 

variability. 

Table 1. PPL Power Capacities Reported in the Literature

A PPL design factors study (Wilkins and Hosni 2011) indicates that, for office buildings, 

PPL peaks could be lower than the traditional 1 W/ft2 presented by ASHRAE (2009), and up to 

2 W/ft2 in the most extreme cases if very dense office equipment use and no diversity are 

assumed. A downward trend in PPL sizing has steadily evolved since the late 1980s, when loads 

Reference Building Type PPL Power Density (W/ft2)

Wilkins and Hosni (2011) Office 0.25 to 2.0 (minimum capacity)

ASHRAE (2009) Office 1 (minimum capacity)

Srinivasan et al. (2011) K-12 education 0.33 to 1.06 (average density)

Metzger et al. (2011) Office 0.9 (average density - cubicle only)

NRDC (2011) Office 7.5 (requested minimum capacity)

(GSA (2011); Haun (2013); GSA 

(2013) Office 4 (requested minimum capacity)
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were assessed from nameplate data and HVAC systems were sized for typical plug load densities 

of 3 to 5 W/ft2

. At five GSA office buildings Wilkins and McGaffin (1994) included individual 

loads and panel measurements and provided evidence of the discrepancy between density 

estimates from nameplate data and actual use. The analysis of PPL densities mentioned by 

Srinivasan et al. (2011) suggests that even 1 W/ft2 is a high estimate. Because of advances in 

energy efficiency and requirements in electronic office equipment, realistic peak PPL densities 

can be as low as 0.25 W/ft2 (Wilkins and Hosni 2011), or lower. Over time, however, a building 

tenant’s level of commitment to energy efficiency can vary, so more conservative PPL sizing 

estimates are often advised (ASHRAE 2009). 

Uncertainties in PPL density assessment stem from guidelines in commercial building 

models and simulations, and from limited availability of benchmarks and case studies that 

confirm simulations. Srinivasan et al. (2011) stress the importance of benchmarking as an 

essential tool to inform and avoid arbitrary or incorrect inputs used in building energy analysis. 

The study compares results from PPL densities with four established assessment approaches: The 

National Renewable Energy Laboratory (NREL), COMNET, ASHRAE 90.1-1989, and 

California Title 24 for classrooms with and without computers. Results show that all four 

approaches over- or underestimate PPL densities over measured values. In particular, PPL 

densities of 1.06 W/ft2 and 0.33 W/ft2 were needed for classrooms with and without computers, 

respectively. 

Case Study: Empire State Building

A 2011 case study on a sustainability and energy efficiency retrofit for the Empire State 

Building in New York City (Empire State Building LLC 2013), and in particular for one of its 

tenants, Skanska (NRDC 2011), highlights lower PPL densities than current leasing energy 

allowance practices. Skanska U.S.A. relocated its New York headquarters to the 32nd floor of the 

Empire State Building. The investments in energy efficiency were based on the 15-year lease 

period, and are expected to save around $300,000 over that time. One outcome of the case study 

relates to tenant incentives. Lease terms can influence tenants to make energy-efficient choices. 

Conventional leases in New York City call for electrical capacity of 7.5 W/ft2, but Skanska’s 

project team calculated that the office would need 2 W/ft2

. As the lease was negotiated, Skanska 

was cautious about adjusting its terms to such a low capacity, seeing no benefit (and potential 

risks) in doing so. Skanska’s landlord helped address these concerns by deploying a new “use it 

or lose it” clause. Tenants are not prevented from using the full electrical capacity in their leases, 

but if they do not consume the electricity after a period of time, they must either pay to keep it in 

reserve or lose the right to excess watts per square foot.

Case Study: U.S. Environmental Protection Agency Region 8 Headquarters

A plug load behavioral change demonstration project (Metzger et al. 2011) for the U.S. 

Environmental Protection Agency’s Region 8 Headquarters included a benchmark study of PPL 

densities. Fully occupied in January 2007, the 420,000-ft2

, nine-story building houses 

approximately 775 employees. The building participated in a research study quantifying the 

effects of various mechanical and behavioral change approaches to PPL energy reduction. An 

inventory of PPL equipment for all participants was taken at the beginning and end of the study. 

A walk-through of the offices was conducted in January and July of 2011, preceding and 

following the experimental phase. Equipment wattages were estimated, because interaction with 

the occupants was restricted, and diversity factors were applied based on ASHRAE 

recommendations (ASHRAE 2005). Diversity factors take into account that all pieces of 
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equipment are not always in use at the same time, and provide a more accurate representation of 

actual operating loads. Average cubicle sizes were 80 ft2 with an average total connected 

equipment load of 145 W without diversity and 71 W with diversity. Average cubicle equipment 

power densities were 0.9 W/ft2 with diversity factors.

The scopes of these studies were limited. Early studies were based on equipment 

nameplate data only. More recent studies have either: (1) focused on an isolated building 

(limiting the broad applicability of the data); or (2) employed meters at the cubicle level only 

(missing many PPLs distributed throughout the building). This report aims to fill in the gaps that 

previous studies missed and thereby improve leasing practices.

Review of Current Leasing Practices and Cost Structures

During the 2012 Commercial Buildings Energy Alliances (now called the Better 

Buildings Alliances) Efficiency Forum industry members from the commercial real estate sector 

stated: “We are putting far more capacity in buildings and creating a lot less efficient systems 

than we could because brokers are telling tenants they need 12, 14, 16 watts per square foot. That 

becomes part of the lease structure...” (CBEA 2012). 

Clayton Ulrich (senior vice president of Engineering Services at Hines) noted that Hines’ 

HVAC designers are fairly comfortable with their current assumptions of 2.5 W/ft2 for PPLs and 

1 W/ft2 for lighting. The combination is used as part of the basis for sizing cooling systems. 

Ulrich (2013) added that the sizing of a building’s electrical infrastructure varies from market to 

market; tenants in different regions expect different W/ft2 for plug loads from the distribution 

transformers; 8 W/ft2 is the default if Hines does not know the market. Furthermore, Tony 

Malkin and Duane Desiderio (Skanska) mentioned a retrofit project in which they achieved less 

than 2 W/ft2 in their tenant buildout when the original request was for 7 W/ft2

. 

Industry collaborators were interviewed to document cost structures for sizing electrical 

infrastructure and HVAC systems. During an interview with Rick Haun (GHT Limited 

Consulting Engineers) (Haun 2013), he was asked “Is the sizing of electrical infrastructure and 

HVAC systems based on W/ft2 requested by tenants?” His response indicated that better 

equipment design maintains good part load efficiency and that there was a capital cost penalty 

for oversizing. 

Methods

Although many sets of building data were available for use, only a few buildings had the 

PPL disaggregation (through submetering) from other building loads. The following criteria were 

used to make the final building selections: 

• Separate metering of PPL energy. Strong candidates include those where “total” PPL 

energy is (or will be) separately metered from other end uses (e.g., lighting and HVAC).

• Separation by space use type. Ideally, any single measured value of total PPL energy is 

associated with just one major space type or business type (e.g., law enforcement space is 

metered separately from medical offices). If that is not possible, the next best case would 

be if types are mixed only minimally and differences are well documented.

• Space use type applicability to others. Strong candidates include spaces that are of 

interest to a large audience. Different types of office space, for example, are a primary 

target because they apply to many users. Other spaces of interest may vary with sector; in 
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higher education, for example, spaces of interest could include (but are not limited to) 

office, laboratory, and housing.

• Knowledge of conditions on site. Strong candidates will be able to document the loads 

and space use types associated with their meters. 

• Resource requirements. More buildings can be considered for inclusion if their data are 

well aligned with project requirements and if the additional analysis can be completed 

within the project budget. In most cases, stronger candidates will be those with less need 

for on-site visits or those where on-site actions can be conducted by members.

Final Selections

Table 2 lists the data sources that were selected. Large office, small office, higher 

education (office and classroom), municipal office, and single- and multitenant office spaces are 

all represented.

Table 2. Finalized Data Sources

 a Data from a commercial office building with net-zero energy goals.

Data 

Source

Number of 

Buildings

Existing 

or New 

Metering Building Types Represented

Level of Data 

Being 

Monitored

NREL 2 Existing

Office – Single Government 

Tenanta

Office – Single Government 

Tenant w/ Data Centera

Whole panel

U.S. 

Dept. of 

Defense 

(DOD)

1 New Office – Single Government 

Tenant

Branch circuit

Receptacle

Stanford 

University7 Existing

Higher Education – Classrooms, 

Meeting Areas, and Faculty 

Offices

Whole panel

Smarte 

Building 10 Existing

Office – Multitenant w/ Data 

Center

Office – Multitenant

Office – Municipal

Office – Single Tenant w/ 

Warehouse

Office – Single Corporate Tenant 

w/ Data Center

Office – Single Corporate Tenant 

w/ Kitchen

Office – Single Corporate Tenant 

w/ Laboratories

Branch circuit

GSA/

Hines 1 New Office – Single Government Tenant Branch circuit
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U.S. Department of Defense Office Building

This 18,818-ft2 facility has approximately 90 occupants and is a typical DOD office 

environment. The building is composed of several space types such as cubicles, offices, kitchens, 

print rooms, and conference rooms. Table 3 describes the total number of space types throughout 

the building.

Table 3. Total Space Types Present in U.S. Navy Office Building

Space Type Total

Libraries 1

Cubicles 57

Offices 30

Kitchens 3

Open Areas (Hallways) 12

Print Rooms 1

Conference Rooms 2

Mail Rooms 1

Reception Areas 1

Metering was deployed in this building to disaggregate PPLs from other building energy 

end uses. DOD traced all the PPL circuits in the building to confirm that the electrical panel 

schedules are accurate. One hundred eighty-four current transducers were installed in the 

building’s electrical panels to submeter all PPL branch circuits. Additionally, 115 receptaclelevel meters were installed to capture more than 95% of individual equipment loads. Utility bills 

made it possible to determine the proportion of PPLs to whole-building energy consumption. 

Figure 2 illustrates the metering installed in this building.
7

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Figure 2. Metering that was installed in a DOD office building (Photo credit: Marjorie Schott, NREL)

U.S. General Services Administration-Occupied/Hines-Managed Office Building

This 18,755-ft2 facility has approximately 60 occupants and is a typical GSA office 

environment that is representative of the larger building stock. The building is composed of 

several space types, including cubicles, offices, kitchens, print rooms, and hearing rooms. 

Table 4 describes the total number of space types throughout the building.

Table 4. Total Space Types Present in U.S. Navy Office Building

Space Type Total

Cubicles 34

Offices 29

Kitchens 1

Open Areas (Hallways) 5

Print Rooms 1

Hearing Rooms 4
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Metering was deployed in this building to disaggregate PPLs from other building energy 

end uses. Nine current transducers were installed in the building’s electrical panels to submeter 

all PPL branch circuits.

Data Validation

The datasets collected were analyzed using the data validation approach developed by 

Sheppy et al. (2013). The key elements of this approach are summarized below:

• If less than one hour of data were missing, linear interpolation was used to fill in data. 

• If more than one hour of data were missing, data from a typical hour during that same 

time of day or day of week were used to fill in the gap. 

• Data that were out of bounds (including negative values) were replaced with valid data. 

• Extreme meter spikes were flagged based on whether they were three standard deviations 

(or more) above or below the average value for that meter. Simple, linear interpolation 

was used to fill extreme meter spikes. 

After the data were validated, meters were aggregated resulting in key building 

performance parameters, such as PPL energy use intensity (W/ft2

), HVAC energy use intensity 

(W/ft2

), and total annual PPL energy consumption (kWh/year). 

Table 5. Measured Average and Measured Peak PPL Energy Use Intensity

Building Type

Average 

(W/ft2)

Peak 

(W/ft2)

Total 

Area 

(ft2)

No. of 

Bldgs.

Office - Single Government 

Tenant 0.24 0.52 18,818 1

Office - Single Government 

Tenant 0.16 0.55 138,000 1

Office - Single Government 

Tenant w/ Data Center 0.34 0.51 18,755 1

Office - Single Government 

Tenant w/ Data Center

- Data center only

0.77 1.25

220,000 1

0.57 0.82

Higher Education - Classrooms, 

Meeting Areas, and Faculty 

Offices

0.23 0.41 115,110 1

0.30 0.64 49,360 1

0.16 0.42 83,130 1

0.40 1.08 26,326 1

0.28 0.63 113,584 3
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Findings

Findings from this PPL capacity analysis strongly suggest that actual PPL densities in 

leased buildings are substantially lower than are usually requested. Table 5 summarizes the 

measured average and measured peak PPL densities of four office buildings and seven higher 

education buildings. On average, the peak-divided-by-average PPL factor is 2.03 for office 

buildings and 2.30 for higher education buildings. This suggests that the buildings that were 

metered in this study are not doing a good job of shutting down PPLs during unoccupied hours. 

This highlights the need for improved plug load controls in these buildings, such as advanced 

power strips. It also shows that for most buildings, the peak density is less than 1 W/ft2 and in all 

cases was below 2 W/ft2. 

Table 6 summarizes the measured average PPL densities of 10 additional office buildings 

that had average data, but not peak data. If we apply the peak-divided-by-average factor (2.03) 

from above, we can estimate that these 10 office buildings also have peak PPLs well below the 5 

to 10 W/ft2 that is typically requested in leases.

Table 6. Measured Average PPL Energy Use Intensity

Building Type

Average 

(W/ft2)

Total 

Area 

(ft2)

Office - Multi-Tenant w/ Data Center 1.17 50,725

Office - Multi-Tenant w/ Data Center 0.19 365,000

Office - Multi-Tenant w/ Data Center 0.37 191,799

Office - Multi-Tenant 0.49 173,302

Office – Municipal 0.40 172,000

Office - Single Tenant w/ Warehouse 0.19 94,621

Office - Single Corporate Tenant w/ Data Center 0.58 97,500

Office - Single Corporate Tenant w/ Data Center 0.36 195,721

Office - Single Corporate Tenant w/ Kitchen 0.64 91,980

Office - Single Corporate Tenant w/ Laboratories 2.27 222,616

Conclusions

Through our measurement and analysis of actual PPL densities over a range of 

commercial building types, we have documented significantly lower (by a factor of 5 to 10) peak 

PPL densities than what is typically requested, negotiated, or required in leases. On average, the 

peak PPL energy use intensities for offices (without laboratories or data centers) is 0.50 W/ft2, 

and 0.64 W/ft2 for higher education buildings; the peak PPL energy use intensity for offices with 

data centers is 0.88 W/ft2. On average, the average PPL energy use intensity for offices (without 

laboratories or data centers) is around 0.28 W/ft2, and 0.27 W/ft2 for higher education buildings. 

Offices with data centers or laboratories do exhibit higher average PPL energy use intensities.

With this evidence in hand, building owners, leasing brokers, and energy managers can 

work toward setting realistic PPL power capacities that are commensurate with actual use. This 
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should lead to the right-sizing of HVAC and electrical systems. Case studies of two buildings 

have shown that right sizing HVAC system components led to an average 14% reduction in 

upfront capital costs and a 3 to 4% reduction in energy costs. 

During construction or in deep retrofits, it is advisable to design flexibility into HVAC 

and electrical systems, allowing for unknown future tenants. For example, rather than oversizing 

the entire system, HVAC distribution pipework and main ductwork can be generously sized to 

allow for larger capacity needs in the future.

References

ASHRAE. 2005. 2005 ASHRAE Handbook-Fundamentals, Chapter 18.

ASHRAE. 2009. 2009 ASHRAE Handbook-Fundamentals, Chapter 18.

CBEA (Commercial Buildings Energy Alliance). 2012. CBEA Efficiency Forum Report. 

Accessed September 20, 2013:

http://www1.eere.energy.gov/buildings/alliances/pdfs/cbea_efficiency_forum_report.pdf

Empire State Building LLC. 2013. Sustainability and Energy Efficiency at the Empire State 

Building. Accessed September 20, 2013: 

www.esbnyc.com/sustainability_energy_efficiency.asp#4.

GSA (General Services Administration). 2013. Standard Lease. GSA Form L201C. Section 3.35: 

Electrical. Accessed September 10, 2013: 

www.gsa.gov/graphics/pbs/Standard_Lease_L201C_6-1-12_final_508c.pdf.

GSA (General Services Administration). 2011. Public Buildings Service. Memorandum for 

Regional Commissioners, PBS Regional Realty Services Officers. Subject: Update of 

Sustainability Lease Provisions and Revised Toilet Room Fixture Schedule. Accessed 

September 10, 2013: www.gsa.gov/graphics/pbs/LAC-2011-

13_Sustainability_Update_final_9-30-11_508c.pdf.

Haun, R. 2013. Telephone Interview. GHT Limited Consulting Engineers. Interview date: 

January 9, 2013.

Metzger, I., A. Kandt, and O. VanGeet. 2011. Plug Load Behavioral Change Demonstration 

Project. NREL/TP-7A40-52248. Accessed December 11, 2012: 

www.nrel.gov/docs/fy11osti/52248.pdf.

NRDC (Natural Resources Defense Council). 2011. Integrated Building and Tenant Space Case 

Study: Skanska and the Empire State Building. Accessed December 11, 2012: 

http://www.nrdc.org/business/casestudies/files/skanskacasestudy.pdf.

Pentland, W. 2011. “GSA Goes Deep Green With Next-Gen Green Leasing Standards.” Forbes 

Magazine. Accessed September 10, 2013: www.forbes.com/sites/williampentland/ 

2011/11/07/gsa-goes-deep-green-with-next-gen-green-leasing-standards/.
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Sheppy, M., A. Beach, and S. Pless. 2013. Metering Best Practices Applied in the National 

Renewable Energy Laboratory’s Research Support Facility: A Primer to the 2011 Measured 

and Modeled Energy Consumption Datasets. Golden, CO: National Renewable Energy 

Laboratory. NREL/TP-5500-57785. 

Srinivasan, R. S., J. Lakshmanan, D. Srivastav, and E. Santosa. 2011. “Benchmarking Plug-Load 

Densities for K-12 Schools.” Proceedings of Building Simulation 2011, 12th Conference of

International Building Performance Simulation Association, November 2011, pp. 2746–

2752.

Thomas, P. C. and S. Moller. 2007. HVAC System Size: Getting It Right—Right-Sizing HVAC 

Systems in Commercial Systems, 2007, Cooperative Research Centre for Construction 

Innovation, p. 11. 

Ulrich, C. 2013. Telephone Interview. Hines. Interview date: January 9, 2013.

Wilkins, C. K. and M. H. Hosni. 2011. “Plug Loads Design Factors.” ASHRAE Journal, May, 

pp. 30–34.

Wilkins, C. K. and N. McGaffin. 1994. “Measuring Computer Equipment Loads in Office 

Buildings.” ASHRAE Journal 36(8):21–24.